Monday, October 10, 2011
Group by Multiple Columns using Anonymous Types in LINQ to SQL
With the power of Anonymous Types, I was able to create a number of reports with different grouping senarios. Anonymous Types as defined in the C# programming guide:
Anonymous types provide a convenient way to encapsulate a set of read-only properties into a single object without having to first explicitly define a type. The type name is generated by the compiler and is not available at the source code level. The type of the properties is inferred by the compiler.
Let’s look at a few ways of Grouping using Anonymous Types. Before we start, displayed below is the sample data used in the queries below:
Simple Group by Anonymous Type – Grouping by Month and Year in a Date
The purpose of this query is to group transactions in the table and retrieve a list of unique months and years in a simple list.var months = from t in db.TransactionData
group t by new { month = t.Date.Month, year = t.Date.Year } into d
select new { t.Key.month, t.Key.year };
Group by Database Column and then by Anonymous Type – Grouping by Expense Category and Monthly Total
The purpose of this query is to group all database records by Category first and then display a Total Expense based on the month in a simple list.var categoryExpense = from t in db.TransactionData
group t by t.Category into g
select new
{
Category = g.Key,
Items = from i in g
group i by new { month = i.Date.Month, year = i.Date.Year } into d
select new { Date = String.Format("{0}/{1}", d.Key.month, d.Key.year ), Amt = d.Sum(s => s.Amount) }
};
Group by Anonymous Type and then by Database Column – Grouping by Month and then by Expense Category and Category Total
The purpose of this query is the opposite of the group query 2. We will first group by the Month and then group by the Category Total:var monthlyExpenses = from t in db.TransactionData
group t by new { month = y.Date.Month, year = y.Date.Year } into g
select new
{
Month = String.Format("{0}/{1}", g.Key.month, g.Key.year),
Items = from i in g
group i by new { i.Category } into d
select new
{
Amt = d.Sum(s => s.Amount)
}
};
With SQL you can seamlessly do all of the above on XML, CSV files or .NET Objects as well.
Recommend Resources to Learn more about LINQ to SQL